J. Org. Chem. 1988,53, 5335-5341 phenylphosphine (526 mg, 20 mmol), and anhydrous toluene (25 mL) which was previously purged with argon and heated for 45 min at 80-81.5 "C. Aliquots were taken at the intervals indicated in Table 11. Each aliquot was quenched by being poured into a mixture of 3 mL of solution A (0.77 g of 1-chloronaphthalene in 100 mL of pentane) and 2 mL of solution B (HC1, 1.2 N) and shaken for 30 s. The organic layers were washed and dried and analyzed by GLC to give the results indicated in Table 11. A blank experiment was performed without palladium acetylacetonateand triphenylphosphine. After 24 h cis-2g remained unchanged. cis-3-MethylcyclohexanolAcetate (10). A shaken mixture of cis-2g (2.92 g, 20 mmol), a catalytic amount of Ra-Ni W2, and ethanol (50 mL) was hydrogenated at atmospheric pressure for 2 h until no more uptake of hydrogen was observed. The mixture was filtered through a short column of Celite and the solvent was fractionally distilled. The residue afforded 2.06 g (66%)of 10: bp 69 O C / l O mmHg; IR (CHClJ 1725 cm-'; 'H NMR (CDCq) 6 0.53-2.10 (m, 9 H), 0.93 (d,J = 5.3 Hz,3 H), 2.02 (s,3 H), 4.464.91 (m, 1H); l 3 C NMR (CDClJ 6 20.78,21.81,23.61,30.98,31.16,37.72, 40.21, 72.67, 169.66.
5335
Acknowledgment. Financial support from CAICYT (Ministerio de Educacidn y Ciencia of Spain) through Grant no. 2014/83 is gratefully acknowledged. R e g i s t r y No. 1, 675-10-5; 2a, 21040-45-9; 2 b , 7204-29-7; 2 c , 6737-11-7;2 d , 31001-80-6;2e, 14447-34-8;2 f , 116504-03-1;cis-2g, 61221-47-4; trans-2g, 61221-48-5; 3 a , 115580-35-3; ( E ) - 3 b , 115580-47-7;(Z)-3b, 115580-49-9;3 ~115580-46-6; , 3d, 115580-36-4; 3e, 115580-37-5; 3 f , 16266-64-1;cis-3g, 116503-95-8; trans-3g, 116503-96-9;3 h , 116503-97-0;3i, 116503-98-1;3 j , 16266-65-2;4a, 116503-99-2;4 b , 115580-48-8;4 f , 16266-55-0;5a, 116504-04-2;6 a , 115580-42-2;6 b , 39849-74-6;6 c , 116504-00-8;6 d , 115580-43-3;6e, 115580-44-4; cis-6g, 116504-01-9; trans-6g, 116504-02-0; 7 , 115580-45-5; cis-8a, 22049-46-3; trans-da, 22031-97-6; cis-10, 116531-33-0; trans-10, 66922-08-5; (E)-H3CCH=CHCH20H, 504-61-0; (E)-HOCH&H=CHPh, 4407-36-7; H&CH(OH)CH= CH2,598-32-3; (E)-H,CCH(OH)CH=CHCH,, 3899-34-1; palladium acetylacetonate, 14024-61-4; 2-cyclohexen-1-01, 822-67-3; 3-methyl-2-buten-l-o1,556-82-1; 4-nitrobenzoylchloride, 122-04-3; cis-5-methylcyclohex-2-en-l-ol 4-nitrobenzoate, 52393-62-1.
Use of Carboxylic Acids as Chiral Solvating Agents for the Determination of Optical Purity of Chiral Amines by NMR Spectroscopy Scott C. Benson, Ping Cai, Marcel0 Colon, Mohammed A. Haiza, Maritherese Tokles, and John K. Snyder* Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215 Received J u l y 27, 1987
Optically pure mandelic acid, Mosher's acid, and N-(3,5-dinitrobenzoyl)phenylglycinehave been used as chiral solvating agents to induce nonequivalence in the 'H NMR spectra of several diamines, amino acid esters, amino alcohols, and other amines. The identity of the chiral solvating agent and the stoichiometry of the solvation complexes that yield the greatest nonequivalence varies with the nature of the substrate. The increasing number of efforts devoted to the design of chiral ligands for metal-promoted reactions in organic synthesis have necessitated the development of methods for measuring the optical purity of both the ligands and the reaction products. The use of specific rotations to determine optical purity can be problematic since rotations vary significantly with the conditions of the measurement, particularly for polar mo1ecules.l We were recently faced with the problem of determining the optical purity of several amino acid esters, p-amino alcohols and vicinal diamines of general structures 1-5 for use as potential chiral ligands in the asymmetric osmium tetroxide oxidation of olefins to vicinal diolsa2 Our initial efforts using the chiral shift reagent Eu(tfc)a were abandoned due to the immediate onset of severe line broadening when the shift reagent was added, even in trace amount^.^ We subsequently found that mandelic acid and other readily ~
(1)For some specific examples: (a) Horn, D. H. S.; Pretorius, Y. Y. J. Chem. SOC.1954,1460. (b) Horeau, A. Tetrahedron Lett. 1969,3121. (c) Kumata, Y.; Furukawa, J.; Fueno, T. Bull. Chem. SOC.Jpn. 1970,43, 3920. (d) Meyers, A. I.; Roth, G. P.; Hoyer, D.; Barner, B. A.; Laucher, D. J. Am. Chem. SOC.1988,110,4611. (2)(a) Tokles, M.; Snyder, J. K. Tetrahedron Lett. 1986,27,3951. (b) Tokles, M.; Snyder, J. K., accepted for publication in J. Org. Chem. (3)For a simiiar example of peak broadening in binaphthyl derivatives in the presence of a lanthanide shift reagent: (a) Brown, K. J.; Berry, M. S.; Waterman, K. C.; Lingenfelter, D.; Murdoch, J. R. J.Am. Chem. SOC. 1984,106,4717.A recent report suggests the use of polar NMR solvents such as acetonitrile-d, to avoid this broadening: (b) Sweeting, L. M.; Crans, D. C.; Whitesides, G. M. J. Org. Chem. 1987,52, 2273.
available, optically pure carboxylic acids (6-8) can be successfully utilized as chiral solvating agents (CSA's) with lH NMR spectroscopy.4 Wonequivalence in the 'H NMR spectrum suitable for integration was achieved under ambient conditions, enabling the measurement of the optical purity.
Results and Discussion Induced Nonequivalence. Nonequi~alence~ was observed in the 'H NMR spectra of the racemic substrate amines 1-5, usually in the signals of the protons adjacent to the amino group, with mandelic acid (6): Mosher's acid (4)For a review of the use of NMR in determining optical purity: Rinaldi, P. L. Prog. Nucl. Mugn. Reson. Spectrosc. 1982,15,291. For recent reviews of chiral solvating agents (a) Pirkle, W. H.; Hoover, D. J. Top. Stereochem. 1982,13,263. (b) Weisman, G.R. in Asymmetric Synthesis; Morrison, J. D., Ed., Academic: New York 1983;Vol. 1, pp 153-172. For a recent report with an excellent reference list: (c) Sweeting, L. M.; Anet, F. A. Org. Magn. Reson. 1984,22,539.For recent reporta on the determination of the enantiomeric purity of primary moncamines using chiral derivatizing agents: (d) Johnson, C. R.; Elliott, R. C.; Penning, T. D. J.Am. Chem. SOC.1984,106,5019.( e )Terunuma, D.; Kato, M.; Kamei, M.; Uchida, H.; Nohira, H. Chem. Lett. 1985,13. (f) Feringa, B. L.; Strijtveen, B.; Kellogg, R. M. J. Org. Chem. 1986,51,5484. (g) Nabeya, A.; Endo, T. J . Org. Chem. 1988,53,3358. (5)The degree of nonequivalence, Ab, is the separation in ppm between the signals experiencing the nonequivalence induced by the CSA. (6)Previous use of 6 as a chiral solvating agent for amines: (a) Dyllick-Brenzinger,R.; Roberta, J. D. J . Am. Chem. SOC. 1980,102,1166.(b) Zingg, S.P.; Amett, E. M.; McPhail, A. T.; Bother-By, A. A.; Gilkerson, W. R. J. Am. Chem. SOC.1988,110,1565.
0022-3263/88/1953-5335$01.50/00 1988 American Chemical Society
5336 J . Org. Chem., Vol. 53, No. 22, 1988
Benson et al. A
A6
1
2
1 d
B
6
4,
p
A6
/-' -,I
(i)-Zb
H*, HN
CO2H
F3G
" Y O H
[(R)-61
Figure 1. Dependence of the A8 induced in 'H NMR spectra of (A) (f)-lc,(*)-4b, and (*)-Fit and (B) (*)-2b and (&)-3a,both in CDCl, on [(R)-6].The A6 values are in units of ppm, the [(R)-6] is in units of mole equivalents relative to the substrates.
\
7 u
8
9 c
H
(7),' or N-(3,5-dinitrobenzoyl)phenylglycine(8)8as chiral solvating agents in CDC1, and other common NMR solvents (Table I).9 While the A6 values could be enhanced by careful adjustment of solvent ratio in a binary or ternary solvent system, in most cases this was not necessary to achieve base-line resolution to monitor optical purity. Nonetheless, the A6 values were sensitive to the solvent composition, and nonequivalence was only observed with 7 in benzene-d, for la, 2a, and 2e. For some substrates, the induced nonequivalence had insufficient resolution for accurate optical purity determination by integration. The only substrate in which we were unable to observe nonequivalence with any CSA was 2c. As expected, the most convenient optical purity determinations were those of the N-methylamino substrates wherein nonequivalence was induced in the methyl singlets. Attempts to utilize (R,R)-(+)-tartaric acid, (R~)-2,3-di-O-benzoyltartaric acid,1° and (1R)-(-)-10-camphorsulfonicacid as chiral solvating agents with several diamines were unsuccessful. The (7)Previous use of 7 as a chiral solvating agent for amines, ref 6, also: (a) Baxter, C. A. R.; Richards, H. C. Tetrahedron Lett. 1972,3357.(b) Maryanoff, B. E.; McComsey, D. F. J. Heterocycl. Chem. 1985,22,911. (c) Villani, F. J.; Costanzo, M. J.; Inners, R. R.; Mutter, M. S.; McClure, D. E. J . Org. Chem. 1986,51, 3715. (8) N-(3,5-Dinitrobenzoyl)aminoacids and their derivatives have been used as chiral bonded phase for chiral HPLC columns. For their use as chiral solvating agents: (a) Pirkle, W. H.; Tsipouras, A. Tetrahedron Lett. 1985,26,2989.(b) Pirkle, W.H.; Pochapsky, T. C. J . Am. Chem. SOC. 1986,108, 5627. (9)For racemic substrates, it is critical not to confuse nonequivalence induced by a CSA and the nonequivalence of enantiotopic ligands adjacent to a chiral center. The enantiotopic N-methyl resonances of the racemic as well as the optically pure amino alcohols 5 are base line separated singlets, presumably due to slow inversion of the nitrogen caused by intramolecular hydrogen bonding. Upon formation of the hydrogen chloride salt, the methyl resonances appear as doublets coupled to the NH proton. In the presence of 6,the 'H spectrum of optically pure 5 reveals one singlet (6 H)for the N-methyl groups. In contrast, racemic 5 yields two singlets (3H each) in the presence of 6. Addition of optically pure amine to this racemic sample in the presence of 6 led to an increase in the intensity of one of the two nonequivalent signals, confirming the nonequivalence due to the formation of diastereomeric salts. For enantiomerically enriched substrates, integration alone would suffice to establish that the observed nonequivalence is due to diastereomeric solvation complexes. (10)Mannschreck, A.; Jonas, V.; Kolb, B. Angew. Chem., Int. Ed. Engl. 1973,12,583.
relatively expensive (R)-(-)-2,2,2-trifluoro-l-(9-anthryl)ethanol (9) l1 succeeded in inducing nonequivalence for some but not all of the few substrates examined, (Table I; IC, 2b, 2d, and 3a). Mandelic acid, 6, induced excellent, base line resolved nonequivalence in the N-methyl signals of the binaphthyldiamines l b and IC. Mosher's acid, 7, however, was better than 6 for achieving nonequivalence in the cyclohexanediamines, 2a, 2d, and 2e. Both 6 and 8 were effective for inducing nonequivalence in the amino acid esters 4 and the amino alcohols 5. Only Mosher's acid succeeded for la, wherein nonequivalence was observed in the H-3 proton of the aromatic ring. In some cases, nonequivalence was optimized only with the addition of a drop or two of acetone-d, or methanol-d,, which also improved the solubility of the diastereomeric salts. Stoichiometry. The dependence of the nonequivalence induced by mandelic acid, 6, on the [CSA]/[substrate] ratio was investigated by using racemic IC, 2b, 3a, 4b, and 5 c as models for each class of substrate (Figure 1). Addition of 6 caused downfield shifts in the resonances of concern for both enantiomers of IC, 4b, and 5c. Nonequivalence induced in the N-methyl resonances of the binaphthyldiamine IC and the monoamine 5c, and in the a-proton resonance of the monoamine 4b, increased as 1-1.5 equivalents of 6 were added (Figure 1A). Further addition of 6 increased A6 only marginally. Furthermore, the A6 values for IC observed with 1 equiv of 6 were invariant to dilution within the concentration range of 0.007-0.029 M of the diastereomeric salt. These results emphasize an advantage in using carboxylic acids (e.g. 6) over more weakly interacting CSA's (such as 9) for enantiomeric purity determination of amines: complete formation of diastereomeric salts with maximal nonequivalence may be achieved at high dilution (small amounts of sample) without a large excess of the CSA. The limited solubility of 6 in CDC13, which prevented the measurement of A6 in the presence of a large excess of 6,12 was overcome by the addition of 2 or 3 drops of (11)(a) Pirkle, W.H.; Sikkenga, D. L.; Pavlin, M. S. J. Org. Chem. 1977,42,384. (b) Pirkle, W.H.; Sikkenga, D. L. J. Org. Chem. 1977,42, 1370. (c) Strekowski, L.;Visnick, M.; Battiste, M. A. J. Org. Chem. 1986, 51,4836.
J. Org. Chem., Vol. 53, No. 22, 1988 5337
Carboxylic Acids as Chiral Solvating Agents acetone-ds. In comparison to the nonequivalence observed in the absence of acetone-d,, the observed A6 values for IC upon the initial addition of 6 were smaller. Far greater amounts of 6 could be added in the presence of acetone-de, however, ultimately leading to nonequivalence comparable' to that observed in the absence of acetone-d6 ([6]/ [IC] = 9.8, A6 = 0.052). The (&)-cyclohexanediamine2b, with two strongly basic amino groups, showed an initial downfield shift of the N-methyl resonances as the CSA was added, but without the induction of nonequivalence when the [6]/[2b] ratio was less than 1. Increasing addition of 6 produced overall shielding of the N-methyl groups, and nonequivalence was observed in these signals. The nonequivalence increased as the CSA/diamine ratio approached 2 (Figure 1B). In the presence of acetone-d6 nonequivalence was observed a t an earlier stage of the titration with 6, but a smaller Ali" was achieved even with a large excess of 6. The maximum A6 was observed with 2.0 molar equiv of 6 in the absence of acetone-d6 and 1.5 molar equiv in the presence of 2 drops of acetone-d, per molar equiv of 2b. The nonequivalence induced in the a-protons of (&)-3a was dependent on the concentration of 6, analogous to 2b. With 3a, however, nonequivalence was observed with a lower concentration of 6, (98% pure by 'H NMR (control spectra of representative compounds indicated as little as 0.05% impurity could be detected).
General Procedure for the Monomethylation of Primary Amino Groups: Preparation of lb and 2b.25 To a solution of diamine la or 2a (1.77 mmol) in benzene (10 mL) and pyridine (1.3 mL) under N2, cooled to 0 "C, was added a solution of ethyl chloroformate (4.42 mmol, 0.42 mL) in benzene (1 mL) dropwise over 15 min. T h e reaction mixture was warmed to room temperature and stirred for 2 h. T h e reaction was subsequently quenched by addition of 2 N KOH (10 mL), the organic layer was separated, and the aqueous layer was extracted with benzene (3 X 20 mL). The organic layers were combined and washed with brine, dried (Na2S04),and the solvent removed by rotary evaporation. The residue was chromatographed [flash Si02], giving the corresponding dicarbamates; yields >95%. To a stirred suspension of LiAlH4 (0.403 g, 10.6 mmol) in T H F (10 mL) under Nz, cooled t o 0 "C, the dicarbamate (1.70 mmol) in T H F solution (5 mL) was slowly added via addition funnel. The reaction mixture was subsequently warmed and refluxed for 3 h. After the reaction mixture was cooled to room temperature, excew LiAlH4 was quenched with water (0.4 mL),and then NaOH solution (15%, 0.4 mL) and water (0.12 mL) were added the gray precipitate was filtered and washed with ethyl ether (20 mL). The fiitrate and washings were combined, and the solvent was reduced
(16)Dale, J. A.; Dull, D. L.; Mosher, H. S. J. Org. Chem. 1969,34, 2543. (17)Pirkle, W. H.; Finn, J. M. J . Org. Chem. 1981,46, 2935. (18)(a) Clemo, G. R.; Dawson, E. C. J . Chem. SOC.1939, 1114. (b) Brown, K.J.; Berry, M. S.; Murdoch, J. R. J . Org. Chem. 1985,50,4345. Also, ref 24. (19)Kuhn, R.; Goldfinger, P. Justus Liebigs Ann. Chem. 1929,470, 183. (20)(a) Jaeger, F. M.; Bijkerk, L. Proc. Acad. Sci., Amsterdam 1937, 40, 12. (b) Langer, A. W.; Whitney, T. A. In Polyamine-Chelated Alkali Metal Compounds; Langer, A. W., Ed.; ACS Symposium Series 130, American Chemical Society: Washington, DC, 1974;pp 270-280. (21)Barluenga, J.; Alonso-Cires, L.; Asensio, G. Synthesis 1979,962. (22)(a) Lifshitz, I.; Bos, J. G. Recl. Trau. Chim. Pays-Bas 1940,59, 173. (b) Williams, 0. F.; Bailar, J. C. J . Am. Chem. SOC. 1959,81,4464. (23)Saigo, K.; Kubota, N.; Takebayashi, S.; Hasegawa, M. Bull. Chem. SOC.Jpn. 1986,59, 931. (24)Jung, M. E.;Rohloff, J. C. J . Org. Chem. 1985,50, 4909. (25)(a) Miyano, S.;Nawa, M.; Mori, A.; Hashimoto, H. Bull. Chem. SOC.Jpn. 1984,57,2171.(b) Kashiwabara, K.;Hanaki, K.; Fujita, J. Bull. Chem. Sac. Jpn. 1980,53,2275.
Benson et al. by rotary evaporation. The residues were chromatographed [flash SiOz] to give the known N&'-dimethyldiamines lb2" and 2b;25b yields >85%.
General Procedure for the Permethylation of Amino Groups via the Eschweiler-clarke Reaction: Preparation of IC, 2d, and 3b.% A solution of the amine or diamine (1mmol), formaldehyde (37 % aqueous solution, 2.5-fold excess based on the number of methyl groups produced), and formic acid (10 mmol) was heated overnight on a steam bath. T h e reaction mixture was cooled, concentrated by rotary evaporation, made basic with NaOH (2 N solution), and extracted with CHC1, (3 X 20 mL). The combined organic layers were washed with brine and dried (Na2S0,). Evaporation yielded the N,N,N'&'-tetramethyldiamines, which were purified by recrystallization (anhydrous EtOH/benzene, l:l),giving the known lcn (mp 216-218 'C), or chromatography (flash, SiOz), giving the known 2dZobs2' and 3b;26cyields >85%. (i)-N,N,N',"-Tet ramethyl- 1,l '-binaphthyl-2,2'-diamine (IC): 'H NMR (CDC13) 6 7.86 (d, J = 8.8 Hz), 7.81 (d, J = 7.8 Hz), 7.46 (d, J = 8.8 Hz), 7.27 (br t), 7.14 (m, 2 H), 2.46 (s, 6 H); 13C NMR (CDCl,) d 149.74 (s, 2 C), 134.66 (s, 2 C), 129.67 (9, 2 C), 128.40 (d, 2 C), 127.69 (d, 2 C), 126.27 (s, 2 C), 126.06 (d, 2 C), 125.86 (d, 2 C), 123.31 (d, 2 C), 120.59 (d, 2 C), 43.44 (q, 4 C).
General Procedure for the Methylation of Amino Groups via Reductive Formylation: Preparation of 2e and 4d-f.29 A solution of the amine or diamine (10 mmol), formaldehyde (37% aqueous solution, 4-fold excess based on the number of methyl groups produced), and Pd-C (2 g) in 95% EtOH (40 mL) was shaken for 4 h in a Parr hydrogenator (50 l b ~ / i n . ~After ). filtration, the reaction mixture was concentrated by rotary evaporation, made basic with NaOH (2 N solution), and extracted with CHCl, (3 X 20 mL). The combined organic layers were washed with brine and dried (Na2S04). Evaporation yielded the permethylated amines, which were purified by chromatography (flash Si02);yields >95%. Known compounds: 4d,29 4e,26aand 4f.29
trans -N,N'-Dimethyl-N,"-diphenylcyclohexane-1,2-diamine (2e): colorless oil; 'H NMR (CDCl,) 6 7.20 (dd, J = 8.8, 7.2 Hz, 4 H), 6.69 (d, J = 8.8 Hz, 4 H), 6.68 (t, J = 7.2 Hz, 2 H), 3.78 (m, 2 H), 2.52 (s, 6 H), 1.85-1.95 (m, 4 H), 1.5-1.6 (m, 2 H), 1.40 (m, 2 H); 13C NMR (CDCl3) 6 149.94 (s, 2 C), 129.06 (d, 4 C), 116.05 (d, 2 C), 112.63 (d, 4 C), 59.83 (d, 2 C), 30.97 (t, 2 C), 29.20 (q, 2 C), 25.49 (t, 2 C); HRMS, [M + l]', calcd for C&InNz 295.2174, found ( m / z )295.2174. General Procedure for the Preparation of 5a-d. T o a solution of the N,N-dimethylamino acid ester (10 mmol) in anhydrous ethyl ether (50 mL) under N2, cooled to 0 'C, was added dropwise n-BuLi (3.3 equiv in hexane) with stirring. The reaction mixture was stirred for 6 h a t room temperature, and then the excess n-BuLi was quenched with water. Additional water (20 mL) was added, and the layers were separated. The aqueom layer was extracted with ethyl ether (4 X 10 mL), and the combined organic layers were washed with brine and dried (Na2S04). The solvent was removed by rotary evaporation and purified by chromatography (flash S O z ) ; yields >95%. 5a: colorless oil; 'H NMR (CDCI,) 6 5.22 (br, OH), 2.54 (s, 6 H), 2.27 (d, J = 10.2 Hz), 2.02 (m), 1.68 (m), 1.52 (m), 1.2-1.4 (10 H), 1.03 (t, J 6.6, 6 H), 0.92 (t, J = 7, 6 H); 13C NMR (CDCl3) 6 73.49 (s), 72.92 (d), 43.65 (br d, 2 C), 37.27 (t), 36.87 (t), 28.46 (d), 26.12 (t),25.63 (t),23.84 (t), 23.50 (t), 23.50 (q), 22.25 (q), 14.26 (q,2 C); HRMS, [M + 1]+, calcd for C15H34N0244.26404, found ( m / z )244.26403. 5b: colorless oil; 'H NMR (CDCI,) 6 7.36 (d, J = 8 Hz,2 H), 7.3 (m, 3 H), 3.30 (s), 2.22 (s, 6 H), 1.7 (m, 2 H), 1.2-1.4 (m, 7 H), 1.1 (m, 3 H), 0.91 (t, J = 7 Hz, 3 H), 0.75 (t, J = 7 Hz, 3 H), OH too broad to be observed under ambient conditions a t 400 MHz; 13C NMR (CDC13)6 135.09 (s), 131.29 (d, 2 C), 127.46 (d, 2 C), 126.97 (d), 78.18 (s), 74.09 (d), 44.39 (9, 2 C), 36.44 (t), 36.05 (t), (26)(a) Clarke, H. T.; Gillespie, H. B.; Weisshaus, S. 2. J. Am. Chem. SOC.1933,55,4571.(b) Pine, S. H.; Sanchez, B. L. J . Org. Chem. 1971,
36,829. ( c ) Horner, L.:Dickerhof, K. Justus Liebim Ann. Chem. 1984, 1240. (27)Mislow, K.; Glass, M. A. W.; O'Brien, R. E.; Rutkin, P.; Steinberg, D. H.;Weiss, J.; Djerassi, C. J . Am. Chem. SOC.1962,84,1455. (28)Madgzinski, L. J.; Pillay, K. S.; Richard, H.; Chow, Y . L. Can. J. Chem. 1978,56,1657. (29)Bowman, R. E.;Stroud, H. H. J . Chem. SOC.1950,1342.
J. Org. C h e m . 1988,53, 5341-5343 26.17 (t),25.61 (t),23.67 (t),23.15 (t),14.19 (q), 13.91 (9); HRMS, [M I]+,calcd for C18H32N0278.24839, found ( m / z ) 278.25068. 5c: colorless oil; 'H NMR (CDClJ 6 7.3 (m, 5 H), 3.03 (dd, J = 10, 4 Hz), 2.87 (dd, JAB = 14.4 Hz, J = 10 Hz), 2.75 (dd, JAB = 14.4 Hz. J = 8 Hz).2.32 (s. 6 H). 1.65 (m).1.4-1.5 (m. 4 H). 1.2-1.4 (m', 7 H), o.gi'(t, J =' i H Z , 'H), ~ ohi it, J = 7 Hz; 3 Hjj OH too broad to be observed under ambient conditions at 400 MHz; 13CNMR (CDCl,) 6 141.04 (s), 129.05 (d, 2 C), 128.27 (d, 2 C), 125.93 (d),74.50 (s), 70.11 (t),44.11 (9, 2 C), 36.62 (t),35.96 (t),25.68 (t), 25.55 (t),23.71 (t),23.42 (t),14.14 (q, 2 C); HRMS, [M + 1]+,calcd for Cl&134N0292.26404, found ( m / z ) 292.26310. 5 d 'H NMR (CDC13)6 3.8 (br, OH),2.52 (4, J = 7.2 Hz), 2.27 (s, 6 H), 1.55 (m), 1.2-1.4 (m, 11 H), 0.91 (d, J = 7.5 Hz, 3 H), 0.87 (t,J = 7.2 Hz, 3 H); 13C NMR (CDCl,) 6 75.98 (s),69.02 (d),
+
5341
36.94 (t), 34.93 (t), 25.43 (t), 25.16 (t),23.04 (t), 22.87 (t),14.04 (q), 13.97 (q),9.11 (q), N(CH3)2)swere severely broadened (6 43 and 45) under ambient conditions at 100 MHz; HRMS, [M + 1]+, calcd for C13H3,N0216.23274, found ( m / z )216.23404.
Acknowledgment. We thank the National Institutes of Health (Grant GM-38014), the Research Corporation, the donors of The Petroleum Research Fund administered by the American Chemical Society, The Camille and Henry Dreyfus Foundation, and Boston University Seed Grant Committee for support. We also thank John Lloyd and Dr. Gerd Dielmann of Finnigan-MAT and Michael Creech of Boston University for the high-resolution mass spectra.
Notes A Novel Ring System: Ga-Aminofuro[2,3-b]furans
Scheme I NC
Vicente J. ArGn,' Nazario Mar&, Carlos Seoane,* and Jose L. Soto
A,
Departamento de Quimica Orghnica, Facultad de Qulmica, Universidad Complutense, 28040-Madrid, Spain
NC
AI
2.-c
Juliana Sanz-Aparicio and Feliciana Florencio Departamento de Rayos X , Instituto Rocasolano, C.S.Z.C., Serrano 119, 28006-Madrid, Spain
1
Received March 15, 1988
Although a fair amount of work has been published on heterocycles containing two fused five-membered rings, less is known about compounds in which furan rings are involved.'V2 The parent furo[2,3-b]furan system and substituted derivatives are apparently unknown. We report in this paper the reaction of bromomalonitrile (1) with o-cyanoacetophenone (2a)in the presence of alkoxide from which a furo[2,3-b]furan results in a single step (Scheme I). The reaction is easily performed in ethanol at room temperature by stirring a mixture of 2a and bromomalononitrile (I). A crystalline solid is obtained in moderate yield (30%). The microanalytical and mass spectral data correspond to two units of w-cyanoacetophenone per unit of malononitrile. An unambiguous structural assignment could not be achieved from the analytical and the deceptively simple spectral data alone, and X-ray crystallographic analysis was therefore performed. Compound 3a was found to be a novel furo[2,3-b]furan heterocyclic system, containing a most unusual functional grouping a t carbon 6a (-0-C(NH2)-O-), a primary amide acetal. A perspective drawing of 3a is shown in Figure 1,with the atomic labeling. The molecule presents a pseudo mirror plane. Each half is nearly situated in a plane, the dihedral angle being about 119.5'. Both five-membered rings are planar. Rings I and I1 and the CI6-N1, nitrile group are nearly planar. On the contrary, rings I11 and IV and the Czo-N17nitrile group are farther from planarity 'Present address: Instituto Quimica Mgdica, C.S.I.C., Juan de la Cierva 3, 28006-Madrid, Spain.
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(see paragraph a t the end of the paper about supplementary material). This nonsymmetrical molecular geometry in the solid state is probably a requirement of the molecular arrangement in the crystal; the NMR spectra suggest a perfect symmetry in solution, however. The reaction can also be applied to substituted o-cyanoacetophenones. The corresponding compounds 3 can be very easily isolated by simple filtration in moderate yields. The presence of electron-donating groups (e.g., methoxy) in the para position of the w-cyanoacetophenones seems to prevent this reaction. (1) Cava, M. P.; Lakshmikantham,M. V. "TwoFused Five-Membered Rings, Each Containing One Heteroatom". In Comprehensiue Heterocyclic Chemistry; Katritzky, A. R., Rees, C. W., Eds.; Pergamon: New York, 1984; Vol. 4, p 1037. (2) Fujimaki, T.;Nagase, R.; Yamaguchi, R.; Otomasu, H. Chem. Pharm. Bull. 1985,33,2663.
0 1988 American Chemical Society
